An ultrasonic atomizer nozzle can change a stream of liquid to a plume of dispersed droplets, whose sizes are significantly uniform and whose kinetic energy are at a minimum. The droplet size is based on the resonant frequency of the nozzle and certain properties of the liquid such as surface tension and density. The minimal kinetic energy of the atomized plume results from the droplets falling off the tops of liquid waves in a film that is formed at an anti-node or distal end of the nozzle. This is done through the use of a uniquely shaped horn designed to achieve a target resonate frequency, the use of piezo-electric transducers configured to convert the input of an alternating or time-varying signal to a mechanical resonance in the subassembly, and a means for connecting the driving signal to the transducers, generally through one or more electrodes.
Atomization occurs at the lowest power levels when the frequency of the driving signal matches the nozzle's natural resonant frequency. Required power levels are significantly affected by many conditions, such as, for example, introduction of liquid to the flow channel and to the atomizing surface, the mass of that liquid and its viscosity, changes in temperature of the materials in the complex subassembly that change the wavelength of the material and, therefore, the resonant frequency, accumulation of foreign materials such as dirt or spray residue on the nozzle's front horn stem or other active horn surface, etc.
Traditionally, a constant power is delivered by an ultrasonic generator to the nozzle from analog electronic driving circuits. These analog driving circuits require time to obtain frequency lock to the nozzle, which may require 500 milliseconds or longer. As such, these ultrasonic generators cannot dynamically react to changing load conditions of the nozzle, such as, for example, impedance, frequency, etc., in a manner that is both fast and stable while providing optimal atomization performance.
Therefore a need exists for a dynamic ultrasound generator for ultrasonic spray systems that quickly and accurately adjusts for different nozzle load conditions using programmable digital circuits.